After their extraction from a nuclear reactor, nuclear fuel elements are stored for a while in a pool for a first cooldown in radioactivity. One is then confronted with the choice of storing or recycling.
To facilitate storage, it is desirable to reduce the bulk of the fuel structure by separating the needles or rods containing the fuel into one group, and any mechanical structure (base or head end sections, guide tubes, supporting grids, etc.) in another.
The above structure has previously been made radioactive by its passage inside the reactor (neutron activity causing the presence of cobalt 60 created by naturally-occurring nickel), but is hardly contaminated, if at all. To limit the space occupied by this structure, it is worthwhile cutting it into pieces which are then stored in canisters.
The reprocessing cycle starts by the shearing of fuel elements in view of dissolving the fuel present in the rods.
It is thus apparent that in most cases a shearing operation is called for along the way.
Devices used for implementing these operations include a shear and a magazine for supplying the shear.
It is here reminded that the fuel elements for PWR or PWA type reactors, i.e., the most widespread type, are formed from a bundle of rods (diameter of the order of a centimeter, length: several meters, number: several hundreds) arranged in parallel and maintained between two fairly massive end pieces.
Thin sheet metal grids are provided between the end pieces to maintain the spacing between the rods.
It is also common practice to have a sheet metal skirting soldered to the base end piece surrounding the base of the fuel bundle.
Shears for fuel elements have already been described.
U.K. Patent GB 1 314 803 describes a so-called horizontal shear in which the fuel elements are placed in a horizontal position for cutting.
French Patent 75 27897 describes a shear in which the fuel elements can be cut out.
It is noted that all of these devices are formed by a chassis in which a saddle is displaceable in an alternating rectilinear movement. The saddle bears a cutting blade on its front face and the chassis contains a fixed counter blade, further frontward. The cutting blade and front counter blade define the cutting plane.
The cutting mode is always identical: the saddle is moved rearward, the fuel element is brought forward between the cutting blade and front counter blade so as to extend beyond the cutting plane by a given amount. The saddle is moved forward and the cutting blade cuts the rods in cooperation with the front counter blade, which prevents them from moving backwards. The saddle is moved rearward, and the cycle is repeated. To facilitate the cutting operation, the bundle is compressed by one or several lateral face clamps that prevent the rods from escaping the cutting action.
The Applicant has noticed that the first cutting operation, which separates the base end section from the rest of the structure, was very awkward. In particular, the presence of a skirting introduces a fault in the cutting operation: the entire rear portion of the skirting is not cut but pushed back into the upper plane of the end piece.
This is owing to the fact that the cutting blade, which is intended to cut perpendicularly to the length of the fuel rods, is not capable of cutting the skirting.